This randomized Demonstration and Education trial will evaluate and compare the effectiveness of a traditional, supervised, group exercise program (Traditional) with a lifestyle physical activity intervention (Lifestyle). The rationale for the study is supported by three main points: 1) It is well established that sedentary habits and low levels of physical fitness are associated with increased risk for morbidity and mortality for several chronic diseases. 2) The prevalence of sedentary habits is high (20 to 25% of the adult U.S. population are sedentary and less than 10% are active at the level recommended by the Surgeon General of the U.S.). Thus, the public health burden of physical inactivity is significant. 3) Long-term follow-up of participants in supervised group exercise programs shows that most individuals revert to their pre- intervention habits during follow-up; therefore, new approaches to physical activity intervention and promotion need to be developed and evaluated. This project will recruit, evaluate, and randomly assign 240 individuals to Lifestyle (60 women, 60 men) and Traditional (60 women, 60 men) exercise intervention groups. both groups will participate in six months of intensive intervention designed to increase their total daily energy expenditure by 3 kcal kg body weight-1 day-1. The Lifestyle group intervention can be briefly described as having a self-managed, problem-solving approach to physical activity intervention, in which activity in integrated into the daily routine. The Traditional group intervention is based on American College of Sports Medicine recommendations for exercise prescription. We hypothesize that both groups will increase their physical activity and improve their physical fitness during the first six months of the project. Both groups will continue for two years of maintenance after the intensive interventions. The primary hypothesis to be tested in the study is that the Lifestyle group will maintain much of the increase in physical activity during follow-up, while the Traditional group will have returned to baseline by the end of the study.